[json] validation doesn't work offline

- VSCode Version: 1.5.1 - OS Version: OS X El Capitan 10.11.3 Every time I launch VS Code when I'm offline, I get this error:  JSON validation doesn't work as a result. I hope a schema reference can be initially cached inside the editor and downloaded once again when internet is on. Steps to Reproduce: 1. Go offline (switch off the internet) 2. Open VS Code. 3. Open some `json` file 4. Work without validation but with an error.